From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ee0-f54.google.com (mail-ee0-f54.google.com [74.125.83.54]) by kanga.kvack.org (Postfix) with ESMTP id CD1B76B0031 for ; Mon, 14 Apr 2014 21:52:37 -0400 (EDT) Received: by mail-ee0-f54.google.com with SMTP id d49so7176288eek.13 for ; Mon, 14 Apr 2014 18:52:37 -0700 (PDT) Received: from zene.cmpxchg.org (zene.cmpxchg.org. [2a01:238:4224:fa00:ca1f:9ef3:caee:a2bd]) by mx.google.com with ESMTPS id m49si23237187eeo.281.2014.04.14.18.52.36 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Mon, 14 Apr 2014 18:52:36 -0700 (PDT) Date: Mon, 14 Apr 2014 21:52:24 -0400 From: Johannes Weiner Subject: Re: [PATCH] mm/memcontrol.c: make mem_cgroup_read_stat() read all interested stat item in one go Message-ID: <20140415015224.GB7969@cmpxchg.org> References: <1397149868-30401-1-git-send-email-nasa4836@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1397149868-30401-1-git-send-email-nasa4836@gmail.com> Sender: owner-linux-mm@kvack.org List-ID: To: Jianyu Zhan Cc: mhocko@suse.cz, bsingharora@gmail.com, kamezawa.hiroyu@jp.fujitsu.com, akpm@linux-foundation.org, cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Hi Jianyu, On Fri, Apr 11, 2014 at 01:11:08AM +0800, Jianyu Zhan wrote: > Currently, mem_cgroup_read_stat() is used for user interface. The > user accounts memory usage by memory cgroup and he _always_ requires > exact value because he accounts memory. So we don't use quick-and-fuzzy > -read-and-do-periodic-synchronization way. Thus, we iterate all cpus > for one read. > > And we mem_cgroup_usage() and mem_cgroup_recursive_stat() both finally > call into mem_cgroup_read_stat(). > > However, these *stat snapshot* operations are implemented in a quite > coarse way: it takes M*N iteration for each stat item(M=nr_memcgs, > N=nr_possible_cpus). There are two deficiencies: > > 1. for every stat item, we have to iterate over all percpu value, which > is not so cache friendly. > 2. for every stat item, we call mem_cgroup_read_stat() once, which > increase the probablity of contending on pcp_counter_lock. > > So, this patch improve this a bit. Concretely, for all interested stat > items, mark them in a bitmap, and then make mem_cgroup_read_stat() read > them all in one go. > > This is more efficient, and to some degree make it more like *stat snapshot*. > > Signed-off-by: Jianyu Zhan > --- > mm/memcontrol.c | 91 +++++++++++++++++++++++++++++++++++++++------------------ > 1 file changed, 62 insertions(+), 29 deletions(-) This is when the user reads statistics or when OOM happens, neither of which I would consider fast paths. I don't think it's worth the extra code, which looks more cumbersome than what we have. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org